Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$91.31	10.270%	$100.6875	$100.69	$100.70	$100.70
Purchase #2	$123.64	13.114%	$139.8541	$139.85	$139.85	$139.90
Purchase #3	$13.60	5.134%	$14.2982	$14.30	$14.30	$14.30
Purchase #4	$108.81	3.395%	$112.5041	$112.50	$112.50	$112.50
Purchase #5	$145.79	3.125%	$150.3459	$150.35	$150.35	$150.30
Purchase #6	$186.73	9.873%	$205.1659	$205.17	$205.15	$205.20
Purchase #7	$116.25	10.643%	$128.6225	$128.62	$128.60	$128.60
7 purchase totals =	$786.13		$851.4782	$851.48	$851.45	$851.50